SE506657C2 - Method and apparatus for projectile measurement - Google Patents

Abstract

According to a method and a device for deciding relative to a chosen reference system, and without contact, the position, direction or speed-or any combination thereof-for a projectile (10) in its flight through a gas towards a giver target (30), the position of the projectile in a first plane (35) is decided at a certain distance from the target by means of at least three acoustic sensors (S1, S2, S3) arranged in a vicinity of the plane. Acoustic sound waves, emanating from a turbulent gas volume (13, 14, 15) extending essentially straight behind the projectile (10), and/or emanating from a wake or monopole (12, 13) existing essentially straight behind the projectile, are received by means of the acoustic sensors (S1, S2, S3). Time differences for the arrival of the acoustic sound waves to the respective acoustic sensors are measured. The projectile position (x, y; x1, y1) in the first plane is calculated from the time differences. The hit point (25) of the projectile in a target plane (31) through the target (30) is decided with the help of the calculated projectile position in the first plane.

Description

506 657 W 20 25 30 35 or sound waves, which are generated at the point of impact and propagate concentrically in the target around the point of impact. U.S. Patent Publication U.S. Patent No. 5,095,433 discloses a target firing system in which a set of vibration sensors are arranged at different locations on the target plate at known mutual distances. The vibration sensors are arranged to detect vibrations or acoustic waves in the board, when a bullet has hit it, and to output electrical signals to a microprocessor as a result thereof. By registering differences in the time for hit reporting from each sensor, the microprocessor can determine the ball's hit point on the target through triangulation. The result is presented by a synthetic voice via a loudspeaker announcing the shooting result. Systems of this type have the disadvantage that since the sensors are permanently mounted in connection with the target board, they run a great risk of sooner or later being hit by an incoming bullet with consequent destruction of the sensor in question as a result.

In another type of target firing system, non-contact detection of projectile position is used. In this case, non-contact detection means that the sensors used for the detection are arranged at a certain distance from the target, whereby the risk of destruction due to a cultural impact is considerably reduced or even eliminated completely. A number of different systems for such non-contact detection by means of acoustic sensors are today known from, for example, the European patent publications EP-B1-0 259 428 and EP-B1-0157 397, the American patent publications US-A-5,247,488 and US- A-5 349 853, tion SE-B-467 550 and the German patent publication DE-C2-41 06 040. system for high-velocity projectiles, where the projectile's Swedish patent publication In SE-B-439 985 a position determination passage is shown through two parallel planes are detected using three acoustic transducers for each plane. All these inventions relate to the detection of so-called supersonic projectiles, ie such projectiles, which travel faster than the sound in the medium in question (usually air). Such projectiles can, for example, consist of anti-aircraft projectiles for firing at towed air targets, bullets from high-speed small arms, and so on.

Common to the inventions listed above is that they all use the so-called Mach cone, which is formed around a supersonic projectile. The Mach cone is a pressure or bow wave (also called sound bang), which arises due to the Överljuds projectile "catching up" with its own sound waves, whereby a sharp conical pressure change occurs around the projectile. The Mach number M, which is defined as the ratio between the projectile speed and the speed of sound, when the sound bang reaches each sensor, is converted into a fast, almost N-shaped electrical pulse, which can be used to determine time differences between each signal and thereafter. - for example by triangulation - determine the position of the projectile in any plane.Some systems of this type also use other acoustic information such as impact sound or firing sound.

However, far from all projectiles travel faster than the speed of sound (M> 1). Many simpler handguns fire bullets, which travel slower than sound.

For pistols with 9 mm ammunition, for example, a bullet speed of about 300 m / s (M = 0.9) can occur, and the corresponding speed for 5.6 mm ammunition can amount to 250 m / s (M z 0.7). In saloon rifles, speeds as low as (M ~ 0.4) sound projectile or so-called subsonic projectile cannot give rise to a Mach cone or sound bang, the systems described above are not applicable for detecting such projectiles. about 140 m / s occur. The invention The object of the present invention is to enable non-contact measurement of the position, direction or velocity of a projectile - for example a bullet fired at a target from a handgun - without using either firing or hitting sounds for the feed. In particular, the present invention aims at enabling a measurement as above for such projectiles, which travel at a speed which is less than the speed of sound propagation in the current gaseous medium (M <1), and which therefore do not give rise to any sound bang. .

The object is solved by a method and a device with the features which are found in the characterizing part of the appended independent claims. Preferred embodiments of the invention are set out in the appended subclaims.

Brief description of the drawings The invention will be described in more detail in the following with reference to the accompanying drawings, in which Fig. 1 is a schematic side view of the sound generation from a projectile, Fig. 2 is a view of an experimental setup for measuring the projectile position in one dimension Fig. 3 is a schematic frontal view of an embodiment of the invention for measuring the position of the projectile in two dimensions and Fig. 4 is a schematic perspective view of another embodiment of the invention for measuring the position of the projectile in three dimensions.

Detailed description of the invention The following is first an analysis of the mechanisms which give rise to measurable sound from an ultrasound projectile.

The analysis does not claim to be complete in all theoretical respects, but it explains the essential parts of the sound generation and therefore forms a good basis for the rest of the description. Next, an experimental setup is illustrated, which illustrates the detection principle, and finally, preferred and alternative embodiments of the invention are described.

Fig. 1 shows in schematic form a projectile 10, which travels at a speed U through a surrounding medium 11, eg air. The projectile 10 consists, for example, of a rifle bullet. When the projectile's velocity U is less than the speed of sound - ie the Mach number M <1, where M = U / c, no sound bang or conical arc wall around the projectile. c generally occurs, a projectile's acoustic emission (sound stringing) can be divided into three main parts, namely a firing part, an aeroacoustic part, which is caused by flow phenomena around the projectile during its orbit, and a impact or impact part. According to the above, the present invention does not use firing sound or hitting sound, so the analysis focuses on the aeroacoustic part.

For an acoustic projectile, this part contains three contributions according to the so-called Lighthills theory of aeroacoustic sound stringing (see, for example, Mats Ãbom, "Compendium in flow technology", Department of Technical Acoustics, KTH, Stockholm, 1991). pole 12, which arises through the so-called wake 13, which is formed The first contribution consists of a so-called acoustic mono- essentially directly behind the projectile 10. A so-called dipole contribution 14 is caused by the institutional vortex release, which occurs at the rear edge of the projectile. Finally, a so-called quadrupole contribution 15 arises through the free turbulence, which is formed in the wake 13 behind the projectile 10.

According to the invention, the monopoly contribution 12 is used in the projectile measurement, and therefore this will now be studied in more detail. According to the reference above, the sound pressure p from a monopole source in linear motion can be expressed as 10 15 20 25 30 35 506 657 p (hit) = _ â_ POQ å * 41:12 1-M'san * em where po is the rest density in the current medium, volume flow , M 'is the Mach number, between projectile and measuring point and sin (®) = Q is the monopoly t is the time, R is the distance h / R, where h is the distance between projectile and measuring point at t = 0.

The volume flow Q consists of the volume addition per unit time in the wake 13, and if the wake has the cross-sectional area A and the projectile travels at speed U, Q = A17 (2) Ur (1) and (2) and geometric rewrites are obtained ___ poUÅ Û __ l : _ pøUaAy 4 ”å 'J (Uf)' + (l-M ') h * 4» {(U:) * + (1-M *) I »*}” ”A (3) If the sound pressure p is plotted as a function of time t with typical values of A, po, U and c, an N-shaped waveform is obtained, which shows that the sound pressure p amounts to several tenths Pa at the distance h = 1 m and several hundredths Pa at h = This pressure can be considered as a pressure wave, which extends 3 m radially from the wake 13 and moves at the speed of sound. This means, among other things, that this pressure wave will be in front of an acoustic projectile but behind an acoustic projectile.

Thus, sound is generated from an ultrasound projectile with such an effect that it can be detected even at several meters distance from the projectile. The energy content of the sound at different frequencies is briefly examined below, which is of some importance for the resolution in the detection according to the invention described below. (1) to an overpressure, when the time passes from negative values to The sound pressure p in the formula changes from a negative pressure positive values. The pressure change occurs for a few milliseconds 15 20 25 30 35 506 657 seconds. In a known manner, a time course can be transmitted to a frequency spectrum by suitable transformation, and a well-known fact is that the faster the time course, the wider the corresponding frequency spectrum. In the present case, a typical course, when p goes from negative pressure to positive pressure, can be attributed to a frequency spectrum with a fundamental frequency of around 20 kHz. This thus means that the process can be detected in a frequency range which is far above the frequency range audible to humans, for example in the range around 40 kHz. 1: 1. . .

Fig. 2 shows an experimental arrangement for illustrating the detection principle according to the present invention. A projectile 10 is shown in the figure on its journey towards a target, which is not shown in Fig. 2 but which is represented by the reference 30 in Figs. 3 and 4. Two acoustic sensors or sensors S1 and S2, each comprising electronics suitable for current application for reinforcement, signal adaptation, etc., are arranged at a distance of a few meters from each other on either side of the projectile's direction of travel.

The sensors are connected to a control unit 20, for example a conventional personal computer of the PC-compatible type with associated keyboard 21. It should be pointed out, however, that the functions and work which the control unit 20 is arranged to perform and which are described in more detail below, can performed in a variety of hardware and software ways, as will be apparent to those skilled in the art. Furthermore, a commercially available projectile speedometer 23 is connected to the control unit 20. The task of the speedometer is to determine the speed of the projectile 10 in the vicinity of the sensors S1 and S2 and is therefore placed immediately in front of them. The control unit 20 is also connected to a presentation unit 22, which in this case consists of a conventional computer monitor. The task of the sensors S1 and S2 is to detect the previously described pressure wave from the projectile 10, as this passes the sensors through a plane which is located at a certain distance from a target and which is preferably parallel to a target plan through said target. The pressure wave can be detected acoustically for both an ultrasonic and a supersonic projectile according to the results from the above analysis.

In order to be able to detect the pressure wave for determining the projectile position in a well-defined plane, the sensors advantageously have a directional effect, ie they have a sensitivity which is large in the immediate vicinity of the plane but which is significantly smaller outside it. Such a direction-dependent sensor can be constructed, for example, by arranging a number of microphone elements, for example seven, in a so-called microphone array, i.e. an arrangement where the microphone elements are arranged at given mutual distances in such a way that the detection contributions from each microphone element reinforce each other. sound waves, which fall in the desired direction of sensitivity (here: the detection plane), respectively counteract each other for such sound waves, which fall from elsewhere. The contributions from each microphone element can also be weighted electronically. The microphone elements can be of the conventional ceramic type, which utilizes piezoelectric effects in the element material. Achieving direction-dependent sensors by connecting a number of sensor elements, which together provide the desired directional effect, is well known in related technical areas - such as, for example, radar technology - and is therefore not described in more detail here.

The sensors advantageously have a sensitivity peak in the ultrasound range between, say, 30 kHz and 50 kHz. This is advantageous for several reasons. Firstly, it is desirable to prevent, as far as possible, disruptive effects from, for example, firing snaps. Although such firing disturbances have a very wide sound spectrum - even far up in the ultrasonic range - high frequency sounds decrease sharply with distance, and if the sensors are placed far away from the firing point (ie close to the target) and In addition, working in the high-frequency range, the degree of interference from firing noise can be minimized.

Each sensor detects sound at a certain degree of gain within a space angle w and thus each has a detection lobe 32, 33. The relative detection sensitivity has been marked in the figure for the respective lobe. In order to be able to measure the position, both sensors must register sound from the projectile, and thus measurement can take place within the rhomboid, which is limited by the dashed lines.

For reasons of clarity, the lobe width, and thus the distance c in the figure, has been exaggerated. In reality, at a detection frequency of, say, 40 kHz and a distance of 4 m between the sensors, the distance c z becomes 200 mm.

The acoustic signals registered by the respective sensors S1 and S2 are converted into electrical signals, which are passed on to the control unit 20. Conventional amplifying and filtering means can of course be used as required. The control unit 20 is arranged to determine from the signals received from the respective sensors a time offset, corresponding to the difference in running time of the project sound / pressure wave to the respective sensor, which in turn (since the sound propagation speed can be assumed to be constant within current times). and distance intervals) are directly representative of the distances a and b, respectively, from the projectile passage point in the measuring plane to the respective sensors S1 and S2, when a correction has been made for the projectile velocity measured by the speedometer 23.

The time difference can be determined by signal processing in the control unit 20 according to any accepted method. Once the time difference has been determined, the side distances a and b can be determined, if the projectile velocity and the sound velocity are known. However, since it is generally not possible to assume that the projectile passes exactly at the height of the sensors S1 and S2, it is possible with the aid of a pair of sensors as above only to determine a host of possible passage points, which constitute a hyperbola. Such hyperbolas are indicated in FIG.

By using a speedometer 23 and three acoustic sensors S1, S2 and S3, all of which, in analogy to the above, are operatively connected to the control unit 20 and thereby also to the display unit 22, according to the figures, two pairwise measurements can be performed by means of e.g. S1 / S2 and S1 / S3, respectively, whereby two hyperbolas for possible passage points are obtained. between the hyperbolas to unambiguously determine the coordinate (x, y) plane of measurement. If the distance between the measuring plane and the control unit is not arranged to calculate the intersections of the position of the projectile's passage through the sensors S1-S3 and the measuring board 30 is too long, the projectile can be assumed to move linearly between the measuring plane and the measuring board 30. in this case arranged to project at the right angle the measured position on a measuring plane 31 through the measuring board 30 and to indicate the determined measuring result 25 in a suitable manner by means of the presentation unit 22. The control unit 20 may also be arranged to output control signals to external equipment such as a folding mechanism or other result indicating equipment depending on the determined measurement result.

I En 3 E,. Fig. 4 shows a preferred embodiment of the objects S3 arranged as above to measure the position (x1, yl) in a horizontal invention. Three acoustic sensors S1, S2, first plane 35 of a passing projectile on its way to S5, S6 are arranged to measure the corresponding position (X2, y2) in a melting board 30. Another three acoustic sensors S4, plane 36 between the first plane 35 and the target plane 31. All acoustic sensors are operatively connected to the control unit 20, which in turn is operatively connected to the presentation unit 22. The control unit is arranged in analogy to what is described above. combining the measurement signals from the respective sensors to determine the position (x1, y1) and (x2, y2) for the passage of the projectile through the plane 35 and 36, respectively. This makes it possible to detect deviations from perpendicular incidence of the projectile towards the target 30, since the control unit 20 is arranged to determine with the aid of said measured positions the direction of the projectile relative to the normal direction of the target plane. Thus, according to the preferred embodiment of the invention, it is possible, with retained accuracy, also to measure in such projectiles which do not fall at a right angle to the target. 3: J. According to an alternative embodiment of the invention, the system according to FIG. 4 is provided with means (not shown) for measuring the travel time between the passage of the projectile through the plane 35 and 36, respectively. By means of this travel time and a known distance between the planes, the control unit is arranged to calculate projectile velocity and present it appropriately via the presentation unit.

According to a second alternative embodiment, the sensors S4-S6 in FIG. 4 are made redundant by the sensors S1-S3 being designed in such a way that they each have Lya sensitivity lobes instead of one. One lobe is used for measuring projectile noise in the first plane 35, while the other lobe is used for measuring in the second plane 36.

In this case, the planes 35 and 36, respectively, are not parallel to each other. By giving the control unit knowledge of the orientation of the two planes relative to each other and relative to the target plane 31, the point of impact can be determined by geometric calculations.

According to a further alternative embodiment, the measurement system is provided with substantially direction-independent acoustic sensors. In this case, each sensor preferably consists of only one microphone element. The control unit 20 is in this case arranged to register the moment when the time differences between the measurement signals from the respective sensor are minimal. By utilizing the values of the time differences at this moment, the control unit can determine the position of the projectile in analogy with the above.

According to another alternative embodiment, the measuring system is provided with at least one microphone, which is directed towards the firing point, is arranged to register direct sound, which arises during the firing, and is arranged to transmit electrical signals corresponding to the direct sound to the control unit 20. The control unit 20 is arranged using these signals to suppress direct sound components in the various measurement signals in order to thereby reduce the disturbing effect of the direct sound on the measurement result.

According to a further alternative embodiment, each acoustic sensor consists of a single microphone element, which is arranged in an acoustically reflecting environment, preferably in a bowl-shaped reflector. The microphone element is placed in the reflector in such a way (eg in its focal point) that incident acoustic sound waves interact on the microphone element. By directing the aperture of the reflector to the desired direction, ie in the detection direction, a high direction-dependent sensitivity (ie a narrow detection lobe) can be achieved. It is further possible, in analogy to the above, to create two detection lobes by a suitable design of the reflector and by using a preferably wedge-shaped member, which is arranged "above" the microphone element with the task of blocking incident sound waves directly from the front but transmitting incident sound waves. .

An optical fiber acting as an acoustic detector, which is arranged in an acoustically reflecting and concentrating environment, can also be used as the microphone element, in order to achieve a direction-dependent sensitivity. The above description of the invention and its embodiments has been made by way of example and not limitation. The invention can be carried out within the scope of the appended claims in other ways than those described above.

Claims (16)

U 20 25 30 35 506 657 14 PATENT REQUIREMENTS A method of determining the position, direction or velocity of a relatively selected reference system without contact - or any combination thereof - of a projectile (10) as it travels through a gas in the direction of a given target (30), where the positions of the projectile in a first and a second plane (35, 36) are determined at a certain distance from the target for each plane by means of at least three acoustic sensors arranged in the vicinity of each plane (S1, S2, S3, S4, S5, S6), characterized in that acoustic sound waves, originating from a wake or monopoly (13) present substantially immediately behind the projectile (10), are occupied by means of said acoustic sensors (S1, S2, S3, S4, S5, S6), time differences for the the arrival of the acoustic sound paths to the respective acoustic sensors is measured, the positions of the projectile (x1, yl, x2, y2) in said first and second planes (35, 36) are calculated from said time differences and the point of impact (25) (30) of the projectile is determined by the projectile's calculated positions in the first a and the second plane. in a case plan (31) through said case 2. A method according to claim 1, characterized by (10) meeting point (25) (31) is determined by projecting on this target plane the position of the projectile in said target plane (35. (xl, yl, 36). X2, y2) in said first and / or second plan 3. A method according to claim 1 or 2, characterized in that the travel time of the projectile (10) between the (35) and the other (36) projectile velocity is calculated. the first plane is measured, from which W U 20 25 30 35 506 657 15 A method according to any one of the preceding claims, characterized in that (S1, S2, S3), which is used for measuring the position of the projectile (10) (x1, yl) in said first plane (35), is also used for measuring the position of the projectile (x2, y2) in (36). of the same at least three acoustic sensors mentioned second plane 5. A method according to any one of the preceding claims, characterized in that the measurements take place for such a pro- (10), which travels at a speed below the speed of sound propagation in the gas in question. 6. A method according to claim 5, characterized in that said projectile (10) consists of a bullet from a handgun. 7. A method according to any one of the preceding claims, characterized by the recording of acoustic sound waves with a main frequency content in a frequency range exceeding the human audible range. Device for practicing the method according to any one of the preceding claims, characterized by a control unit (20) operatively connected to said acoustic sensor (S1, S2, S3, S4, S5, S5, S6) and a present operatively connected to said control unit. station (22), the acoustic sensors being arranged to detect the passage of the projectile (10) through said first and (35, 36) and, accordingly, emitting electrical signals to the control unit, second plane wherein said control unit is arranged to receive electrical signals from each acoustic sensor, determine mutual differences in time between the respective acoustic sensors' detection of the passing projectile, from 506 657 W Ü 20 25 30 35 16 determine these time differences the projectile's position in the first and second plane, using these positions determine the projectile's point of impact in said target plan (31) and with the help of the presentation unit indicate the established meeting point. Device according to claim 8, characterized (S1, S2, S3, S4, S5, S6) direction-dependent sensitivity and are arranged to detect sound only in said acoustic transducers in or in the immediate vicinity of said first and second planes, respectively. (35, 36). Device according to claim 9, characterized in that each of said acoustic sensors (S1, S2, S3, S4, S5, S6) is constituted by a set of microphone elements, which are arranged at given mutual distances to achieve said directional dependence. sensitivity. Device according to claim 9, characterized (S1, S2, S3, which is arranged in that each of said acoustic sensors S4, S5, S6) at a certain point relative to an acoustically reflecting and consists of a microphone element, concentrating environment for achieving the said direction-dependent sensitivity. Device according to any one of claims 8 to 11, (20) for measuring the running time of the projectile (10) between said characterized in that the control unit is arranged first and second plane (35, 36) and from this determining the velocity of the projectile. . Device according to any one of claims 8 to 12, (20) consists of a computer and in that said presentation unit is characterized in that said control unit (22) consists of a computer monitor. 10 506 657 17 Device according to claim 9, characterized in that at least one of said acoustic sensors (S1-S6) is constituted by a distributed and elongated microphone element. 15. A device according to claim 14, characterized in that said microphone element is an optical fiber. Device according to claim 14 or 15, characterized in that said microphone element is arranged in an acoustically reflecting and concentrating environment to achieve said direction-dependent sensitivity.